Positioning unit and apparatus for adjustment of an optical element

ABSTRACT

The disclosure provides a positioning unit for an optical element in a microlithographic projection exposure installation having a first connecting area for connection to the optical element, and having a second connecting area for connection to an object in the vicinity of the optical element.

The invention relates to a positioning unit for an optical element in amicrolithographic projection exposure installation having a firstconnecting area for connection to the optical element, and having asecond connecting area for connection to an object in the vicinity ofthe optical element.

The invention also relates to an apparatus for adjustment of an opticalelement having an optical axis with respect to an external holder in anobjective structure or with respect to holders which are locatedadjacent to it, with the optical element being connected to the externalholder via a plurality of intermediate parts which are provided withadjustment devices.

With regard to the prior art, reference is made to U.S. Pat. No.5,986,827, US 2002/0163741 A1, US 2002/0176094 A1, WO 2005/026801 A2, DE103 44 178 A1, DE 102 26 655 A1, DE 199 10 947 A1, EP 1 312 965 A1 andEP 1 209 500 A2.

Some of the already known adjustment apparatuses have only a lowcarrying capability, are cumbersome and are of a complex design, and insome cases also promote undesirable oscillation excitations of theoptical element.

One preferred field of use for adjustment apparatuses as described aboveis in a projection exposure installation having a projection objectivefor microlithography, for production of semiconductor elements, sinceextremely accurate imaging qualities are required for this purpose.

However, optical elements can become decentered by manufacturing orinstallation inaccuracies during installation with respect to mechanicalreference surfaces on the holder. Mechanical reference surfaces may, forexample, be centering collars or holder flanges, with respect to whichthe holder is aligned with respect to an objective structure, forexample a projection objective. Reference surfaces such as these arelikewise also used for alignment of individual holders with respect toone another.

Although tilting tolerances can be compensated for by so-calledspherization for example of a lens as an optical element before beingbonded into the internal holder, subsequent process steps after it hasbeen bonded in can nevertheless lead to the lens becoming decenteredwith respect to the reference surfaces on the holder. This can occur,for example, as a result of adhesive shrinkage as the adhesive cures.

With certain holding techniques, for example when optical elements areclamped, a spherization process can be carried out only with greatdifficulty, so that an apparatus is required for adjustment of theoptical element with respect to the reference surfaces on the holder.

The subject of the present invention is to provide a positioning unitfor an optical element, which positioning unit has a high level ofstiffness and in which case positioning should be possible for aplurality of degrees of freedom.

A further subject matter of the present invention is to avoid thedisadvantages of the prior art as stated above, in particular theprovision of an adjustment apparatus in which an optical element can bemoved as far as possible in all six degrees of freedom with respect tothe reference surfaces and can be adjusted appropriately, but in which asufficiently high stiffness level can be maintained despite very preciseadjustment.

According to the invention, in the case of a positioning unit for anoptical element in a microlithographic position exposure installation,this object is achieved by a first connecting area A for connection toan optical element and a second connecting area B for connection to anobject in the vicinity of the optical element, at least two levers,which are connected via their respective lever bearings to the secondconnecting area B, and whose respective load arm is connected by meansof a joint and via an intermediate element C, which acts on this joint,to the first connecting area A, having adjustment devices or actuatorsarranged on the respective force arms of the levers in which, in a firstposition, the first connecting area A and the second connecting area Bare arranged relative to one another such that the lever bearings of theat least two levers and the joints which are associated with theselevers have approximately parallel rotation axes, which lieapproximately on one plane in the first position.

In this case, the first position is advantageously a basic position, anda second position is a deflected position of the levers.

According to the invention, in this case, the first connecting area Amay be a head part which is connected to the optical element directly orvia an inner ring. The second connecting area B may be a foot part,which is firmly connected to an external holder or forms a part of theexternal holder.

The intermediate element C may be at least one moving intermediate part.If an adjustment capability in six degrees of freedom is desired,correspondingly more intermediate elements must be provided.

According to a further subject matter of the invention, in the case ofan apparatus in which an optical element is connected via adjustmentdevices to an external holder, this object is achieved in that eachadjustment device has a foot part, which is arranged on the externalholder and on which moving intermediate parts are arranged and areconnected to adjusting elements in such a manner that first movingintermediate parts can rotate about an axis at right angles to a z-axis,in which the adjusting elements are connected via second movingintermediate parts directly or via a center part to the optical element,in which, in the case of fixed adjusting elements, the second movingintermediate parts which are arranged between the optical element or acenter part and the adjusting elements allow a rotary movement of theoptical element with respect to the foot part about an axis at rightangles to the z-axis.

In this case, the z-axis may advantageously lie on a connecting linebetween the head part, the center part and the foot part.

The z-axis is preferably the optical axis.

A further advantageous refinement provides for the second intermediateparts to be arranged at an angle α to the z-axis.

The positioning unit according to the invention and the apparatus allowexact positioning and—if required—linear movement and tilting of theoptical element with respect to the external holder even immediatelybefore installation in the objective structure, for example, aprojection objective. This means that all of the centering areas of theoptical element with respect to the external holder can be correctedaccording to the invention.

The apparatus according to the invention also makes it possible for theoptical element still to be moved and to be positioned appropriatelyexactly in use after installation of the holder in the objective.

One highly advantageous refinement of the invention consists in that theadjusting elements are connected via the second moving intermediateparts to the center part, with the center part being connected to a headpart which is arranged on an internal holder or on the optical element,and with the center part having at least one third moving intermediatepart being provided in such a manner that the head part can be moved ina direction at right angles to the z-axis with respect to the centerpart, and can be rotated about another axis at right angles to thez-axis and about the z-axis with respect to the center part.

In this case, the axis which is at right angles to the z-axis ispreferably the x-axis, and the other axis is the y-axis.

The arrangement according to the invention of the intermediate elements,which are preferably in the form of solid hinged joints in the form ofleaf springs or levers like leaf springs, results in an adjustmentmechanism by means of which, if required, an optical element can bemoved in up to six degrees of freedom relative to the external holder.

However, in this case, small cross sections, as are present in the priorart, can be avoided in the case of solid hinged joints, as a result ofwhich the overall mechanism is considerably more resistant to shocks andis stiffer, so that it cannot be excited to carry out undesirableoscillations as easily.

Furthermore, the adjustment apparatus according to the invention can bearranged in a very space-saving manner. This applies in particular to alow physical height, which can be achieved by skillful arrangement ofthe solid hinged joints, because, in contrast to conventional adjustmentapparatuses, the guidance for the movement of the adjusting levers oradjusting elements is integrated in the tilting decoupling about thex-axis. This makes it possible to reduce the number of solid hingedjoints, without having to use solid hinged joints with a very smallcross section, which bend easily about two axes. Solid hinged jointswhich bend easily about two axes can withstand only small loads, such asthose which occur in the case of shocks, because of the very small crosssection.

Advantageous developments are specified in the other dependent claimsand will become evident from the exemplary embodiments which aredescribed in the following text, in principle, with reference to thedrawing, in which:

FIG. 1 shows a schematic illustration of projection exposureinstallation;

FIG. 2 shows a perspective view of an adjustment apparatus according tothe invention;

FIG. 3 shows an enlarged illustration of an adjustment device as shownin FIG. 2;

FIG. 4 shows a side view of the adjustment device shown in FIG. 2,illustrating a capability for movement in the y-direction;

FIG. 5 shows a side view of the adjustment device shown in FIG. 4,illustrating a capability for movement in the z-direction;

FIG. 6 shows a side view of a second embodiment of the adjustment deviceshown in FIG. 3;

FIG. 7 shows a side view of a third embodiment of the adjustment deviceshown in FIG. 3;

FIG. 8 shows a side view of a fourth embodiment of the adjustment deviceshown in FIG. 3;

FIG. 9 shows a side view of a fifth embodiment of the adjustment deviceshown in FIG. 3;

FIG. 10 shows an enlarged illustration of a similar embodiment of anadjustment device to that shown in FIG. 3;

FIG. 11 shows a side view of the adjustment device as shown in FIG. 10;

FIG. 12 shows an enlarged perspective illustration of a similarrefinement of an adjustment device to that shown in FIG. 3, with anglesα which are greater than 90 degrees;

FIG. 13 shows an enlarged perspective illustration of a furtherembodiment of an adjustment device with a very small physical height inthe z-direction;

FIG. 14 shows a perspective view of an adjustment apparatus as shown inFIG. 2 from above with adjustment devices which are inclined withrespect to the optical axis;

FIG. 15 shows a perspective view of an adjustment apparatus as shown inFIG. 10 from the side with adjustment devices which are inclined withrespect to the optical axis;

FIG. 16 shows an enlarged perspective illustration of a furtherembodiment of an adjustment device, in which the optical element neednot be rotated about the optical axis;

FIG. 17 shows a side view of the adjustment device which corresponds tothe adjustment device shown in FIG. 5, in which additional detailsrelating to the levers, which are like leaf springs, and the rotationaxes are shown, for explanatory purposes;

FIG. 18 shows a further embodiment of an adjustment device andpositioning unit;

FIG. 19 shows an outline illustration with force and load arms of thelevers and with rotating joints, based on FIG. 18;

FIG. 20 and

FIG. 21 show illustrations of movement capabilities for the exemplaryembodiment shown in FIG. 18;

FIG. 22 shows a further embodiment with greater rotation flexibilityabout the z-axis;

FIG. 23 shows an embodiment similar to that shown in FIG. 22, but in asimpler form;

FIG. 24 and

FIG. 25 show two further embodiments of positioning units;

FIG. 26 shows an embodiment with stiffening in the y-direction;

FIG. 27 shows an embodiment in which the hinged joints connected to theadjusting levers are reinforced;

FIG. 28 shows an embodiment in which adjusting levers as adjustingelements, and hinged joints which interact with them, are likewisereinforced;

FIG. 29 shows an embodiment in which a center part is stiffened in they-direction by means of a jointed coupler;

FIG. 30 shows a detail of an enlargement from FIG. 3 with the twolevers, which are like leaf springs, between the foot part and anotherembodiment of the center part;

FIG. 31 shows a detail from the outline illustration shown in FIG. 19,with another embodiment of a lever bearing; and

FIG. 32 shows a detail of the outline illustration shown in FIG. 19 witha further embodiment of a lever bearing, in a similar form to theembodiment illustrated in FIG. 31.

FIG. 1 illustrates a projection exposure installation 1 formicrolithography. This is used for exposure of structures on a substratewhich is coated with photosensitive materials, and which in generalpredominantly composed of silicon and is referred to as a wafer 2, forproduction of semiconductor components, for example computer chips.

In this case, the projection exposure installation 1 essentiallycomprises a lighting device, 3, a device 4 for holding and exactpositioning of a mask which is provided with a grid-like structure, aso-called reticle 5, by means of which the subsequent structures on thewafer 2 are defined, a device 6 for holding, movement and exactpositioning of this actual wafer 2, and an imaging device, specificallya projection objective 7 with a plurality of optical elements, such aslenses 8, which are mounted via holders 9 in an objective housing 10 ofthe projection objective 7.

The fundamental principle of operation in this case provides for thestructures which are introduced into the reticle 5 to be imaged, reducedin size, on the wafer 2.

After the exposure has been carried out, the wafer 2 is moved onwards inthe direction of the arrow, so that a large number of individual fields,each with the structure predetermined by the reticle 5, are exposed onthe same wafer 2. Because of the step-by-step feed movement of the wafer2 in the projection exposure installation 1, this installation isfrequently also referred to as a stepper.

The lighting device 3 produces a projection beam 11, as is required forimaging of the reticle 5 on the wafer 2, for example light or similarelectromagnetic radiation. A laser or the like may be used as the sourcefor this radiation. The radiation is formed in the lighting device 3 bymeans of optical elements such that the projection beam 11 has thedesired diameter, polarization, wavefront shape and similarcharacteristics on arrival at the reticle 5.

The projection beam 11 is used to produce an image of the reticle 5,which is transferred in an appropriately reduced form by the projectionobjective 7 onto the wafer 2, as has already been explained above. Theprojection objective 7 has a large number of individual refractive,defractive and/or reflective optical elements, such as lenses, mirrors,prisms, closure plates and the like.

As can be seen from FIG. 2, the optical elements, for example the lens8, is mounted in an inner ring 20, which is connected to an externalholder 22 via three adjustment devices 21. The three adjustment devices21 bear the weight of the inner ring 20 and of the optical element,specifically of the lens 8. However, instead of the lens 8, it is, ofcourse, also possible to mount a different optical element in the innerring 20, for example a mirror.

The external holder 22 is firmly connected to adjacent external holdersor to an objective structure, for example to the objective housing asshown in FIG. 1. In this case, interfaces or reference surfaces 22 a, 22b and 22 c of the external holder 22 together with the external holderslocated adjacent to them or together with the objective housing 10represent the reference geometry on the external holder 22, with respectto which the optical element 8 must be aligned. The reference surface 22a on the external holder 22 represents the x₀-direction, with thex₀-axis of the global coordinate system for this purpose being at rightangles to the reference surface 22 a. The x₀-position of the lens 8 withrespect to the external holder 22 can be measured from the referencesurface 22 a.

The reference surface 22 b rests on the outer holder 22 at right anglesto the reference surface 22 a. The reference surface 22 b represents they₀-axis in the global coordinate system and is at right angles to thereference surface 22 b. The y₀-position of the optical elements,specifically the lens 8, can be measured from the reference surface 22b.

The reference surface 22 c rests on the lower face of the externalholder 22, and represents the z₀-axis of the global coordinate system.The z₀-axis represents the optical axis of the projection objective 7.The z₀-position and the tilt about the x₀-axis and y₀-axis, which are atright angles to the z₀-axis, of the lens 8 are measured from thereference surface 22 c.

The reference surface 22 c is also suitable for attachment of theexternal holder 22 to the objective structure.

The arrangements of the reference surfaces 22 a, 22 b and 22 c asillustrated in FIG. 2 should, of course, be regarded only as examples.Within the scope of the invention, it is also possible to use otherarrangements and reference surfaces which, for example, may also bebased on polar coordinates.

Each adjustment device 21 is subdivided into a foot part 23, a centerpart 24 and a head part 25. In this case, the foot part 23 is firmlyconnected to the external holder 22, and the head part 25 is firmlyconnected to the inner ring 20.

As can be seen from FIG. 2 and the enlarged illustration in FIG. 3, eachadjustment device 21 has an x-axis, a y-axis and a z-axis in a localcoordinate system (related to the respective adjustment device).

The local z-axis is located on the connecting line between the head part25, the center part 24 and the foot part 23. The x and y-axes lie on aplane at right angles to this. The z-axis is in general parallel to theoptical axis.

A flexible and/or elastic first intermediate part 26 in the form of aconnection or coupler like a leaf spring connects an adjusting element27 to the foot part 23 such that it can pivot about the x-axis. For thispurpose, the first elastic intermediate part 26 is oriented such that itallows bending about the x-axis. Adjustment screws 28, 29 can be used toset and fix the pivoting angle of the adjusting element 27 with respectto the foot part 23. As can be seen in particular from FIG. 3, the twoadjusting screws 28, 29 are each held in threaded holes in the foot part23. For this purpose, the foot part 23 in this area forms a U-shapedpart, between whose limbs the adjusting element 27 is held. Theadjusting element 27 can thus be clamped in between the ends of the twoadjusting screws 28 and 29. The adjusting element 27 can be pivotedabout an axis in the x-direction by movement of the adjusting screws 28,29.

A flexible and/or elastic connection between the adjusting element 27and the center part 24 is likewise provided by means of a second elasticintermediate part 30 in the form of a connection or coupler like a leafspring. The second elastic intermediate part 30 is positioned at anangle α to the z-axis, and can be bent about the x-axis. Because theshaft, which bends easily, of the second elastic intermediate part 30 isoriented parallel to the local x-direction, it represents a connectionof the adjusting element 27 to the center part 24, which can rotateabout the x-axis and can at the same time move translationally at rightangles to the plane of the elastic intermediate part or leaf spring 30.

In the same manner as in the case of the adjusting element 27 with thefirst intermediate part 26, a first flexible and/or elastic intermediatepart 31, likewise in the form of a connection or coupler like a leafspring, connects an adjusting element 32 to the foot part 23 such thatit can pivot about the x-axis. For this purpose, the first elasticintermediate part 31 is oriented such that it allows bending about thelocal x-axis.

Once again, like the second intermediate part 30, a second elasticintermediate part 33 in the form of a connection or coupler like a leafspring is used as a flexible connection between the adjusting element 32and the center part 24. The second elastic intermediate part 33 ispositioned symmetrically with respect to the second elastic intermediatepart 30 at an angle α to the z-axis, and allows bending about thex-axis. Because the shaft, which bends easily, of the second elasticintermediate part 33 is oriented parallel to the x-axis, it represents aconnection of the adjusting element 32 to the center part 24 which canrotate about the x-axis and is at the same time translational at rightangles to the plane of the second elastic intermediate part 33, or theleaf-spring plane, of this part. The adjusting element 32 is fixed bymeans of adjusting screws 34 and 35 to the foot part 23, which islikewise U-shaped in this area, in the same way as the adjusting element27. At the same time, the position of the adjusting element 32 ischanged by an appropriate movement of the adjusting screws 34 and 35.

The described mounting and guidance of the adjusting elements 27 and 32allows the center part 24 to be rotated with respect to the foot part 23about an imaginary intersection axis of the extended planes of thesecond elastic intermediate parts or leaf springs 30 and 33. Because theshafts, which bend easily, of the second elastic intermediate parts 30and 33 are in this case oriented parallel to the x-axis, theintersection axis which is formed by the planes of the second elasticintermediate parts 30 and 33, and thus also the rotation axis of thecenter part 24 with respect to the foot part 23, is likewise parallel tothe x-axis.

The center part 24 is in turn connected by means of a third flexibleand/or elastic intermediate part 36 in the form of a leaf spring to thehead part 25 such the head part 25 can be moved in the x-direction withrespect to the center part 24 by S-shaped bending of the third elasticintermediate part 36, and can be rotated about the y-axis by a singlebending of the third elastic intermediate part 36. The head part 25 canbe rotated about the z-axis with respect to the center part 24 by meansof torsion on the third elastic intermediate part 36, which lies on theplane of the z-axis.

All the elastic intermediate parts 26, 30, 31, 33 and 36, which are inthe form of leaf springs, are solid hinged joints which are thus in eachcase integral with the parts located adjacent to them and the adjacentparts connected to them. The leaf springs may, of course, also beseparate parts.

The arrangement of the second elastic intermediate parts 30 and 33 withrespect to the first elastic intermediate parts 26 and 31 allowsrotation of the center part 24 and of the head part 25 with respect tothe foot part 23, when the adjusting elements 27 and 32 are held firmly,about an intersection axis which is formed by the planes of the secondelastic intermediate parts or leaf springs 30 and 33.

Since the center part 24 can be rotated about the x-axis with respect tothe foot part 23, and the head part 25 can be moved linearly in thex-direction with respect to the center part 24 and can be rotated aboutthe y-axis and about the z-axis, the head part 25 can also be movedlinearly in the x-direction, and can be rotated about the x, y andz-axes, with respect to the foot part 23.

In one kinematically highly advantageous refinement, the planes of theleaf springs or the planes of the second elastic intermediate parts 30and 33 are positioned with their angles α with respect to the z-axissuch that they intersect at a center point 40 of the leaf springs or ofthe third elastic intermediate part 36 (see FIG. 4). In this way, allthree rotation axes of the head part 25 with respect to the foot part 23pass through the center point 40 of the leaf spring or of the thirdelastic intermediate part 36. This refinement results in each adjustmentdevice 21 fixing only two translation degrees of freedom in the y andz-directions per adjusting element 27 and 32 that is held firmly. Thethree adjustment devices 21 in this manner form a statically definedbearing for the inner ring 20, in a similar manner to that in the caseof a hexapod with three translational and three rotational degrees offreedom. This is achieved in that two translational degrees of freedomcan be adjusted per adjustment device, for example the local z-directionand the local y-direction.

The head part 25 can be moved in the y-direction and in the z-directionwith respect to the foot part 23 for each adjustment device 21 bysetting a pivot angle β of the adjusting elements 27 and 32 by means ofappropriate adjustment by the adjusting screws 28, 29, 34, 35. If theadjusting elements 27 and 32 are pivoted in the same sense, then thisresults in the head part 25 being moved in the y-direction with respectto the foot part 23 (see the arrow 41 in FIG. 4). If the adjustingelements 27 and 32 are pivoted in opposite senses, this results in thehead part 25 being moved in the z-direction with respect to the footpart 23 (see the arrow 42 in FIG. 5).

Thus, as can be seen from FIG. 2, the optical element 8 can be moved inthe x₀-direction and y₀-direction, and can be rotated about the z₀-axis,with respect to the external holder 22, by moving the head parts 25 ofthe adjustment devices 21 in their respective local y-direction.

A z₀ linear movement (optical axis) and tilts about the x₀-axis andy₀-axis of the optical element 8 with respect to the external holder 22can be achieved by movement of the head part 25 of the adjustment device21 in its respective local z-direction.

As can be seen, each adjustment device 21 thus comprises a foot part 23,two adjusting elements 27 and 32, a center part 24 and a head part 25,which are connected to one another via the elastic intermediate parts26, 30, 31, 33 and 36 in the form of leaf springs as solid hingedjoints.

When viewed in the respective local coordinate system, the elasticintermediate parts are in this case arranged such that:

-   -   1. the first elastic intermediate part 26 between the foot part        23 and the adjusting element 27 allows a rotational movement of        the adjusting element 27 with respect to the foot part 23 about        an axis parallel to the local x-direction,    -   2. the first elastic intermediate part 31 between the foot part        23 and the adjusting element 32 likewise allows a rotational        movement of the adjusting element 32 with respect to the foot        part 23 about an axis parallel to the local x-direction,    -   3. the second elastic intermediate part 30 connects the center        part 24 to the adjusting element 27,    -   4. the second elastic intermediate part 33 between the adjusting        element 32 and the center part 24 is positioned at an angle 2α        with respect to the second elastic intermediate part 30, as a        result of which, when the adjusting elements 27 and 32 are        fixed, the second elastic intermediate parts 30 and 33 together        allow only a rotational movement of the center part 24 with        respect to the foot part 23 about an axis parallel to the local        x-direction, and    -   5. the third elastic intermediate part 36 allows movement of the        head part 25 with respect to the center part 24 in the local        x-direction, and rotation of the head part 25 with respect to        the center part 24 about the local y-axis and the local z-axis.

The position of the two second elastic intermediate parts 30 and 33 atan angle 2α with respect to one another, and symmetry with respect tothe local z-axis for each angle α results in the adjustment device 21having a symmetrical design. However, of course, it is also within thescope of the invention to choose different angle settings here.

The choice of the arrangement of the second elastic intermediate parts30 and 33 in such a manner that the extended imaginary planes of thesetwo elastic intermediate parts intersect at the center point 40 of thethird elastic intermediate part 36 is kinematically advantageous.

As can also be seen from FIGS. 3 and 4, the most flexible bending axisof the third elastic intermediate part 36, which represents they-rotational axis of the head part 25 with respect to the center part24, and the torsion axis of the third elastic intermediate part 36,which represents the z-rotation axis of the head part 25 with respect tothe center part 24, passes through the center point 40 of the thirdelastic intermediate part 36. In this way, the x-axis, y-axis and z-axisof the head part 25 with respect to the foot part 23 intersect at thecenter point 40 of the third elastic intermediate part 36, which is likea leaf spring.

FIG. 6 shows a refinement of the third elastic intermediate part 36 inwhich the third elastic intermediate part 36 is formed by two shortleaf-spring joints 36 a and 36 b, which can each be tilted about an axisparallel to the y-direction. The two leaf-spring joints 36 a and 36 bare separated from one another by a center piece 36 c. This refinementincreases the stiffness in the z-direction without decreasing thetranslational flexibility in the x-direction. The longitudinal orbending axes of the leaf-spring joints 36 a and 36 b and those of thecenter piece 36 c run in the y-direction.

However, the refinement according to FIG. 6 somewhat restricts thedesired z-rotation mobility of the head part 25 with respect to thecenter part 24. For this reason, the exemplary embodiment shown in FIG.7 proposes that the center piece 36 c be provided between the twoleaf-spring joints 36 a and 36 b with slots 43 which preferably run inthe z-direction. The slots 43 may be formed virtually continuously asfar as the center, or else may represent only short incisions. As can beseen from FIG. 7, a large number of slots 43 are arranged parallelalongside one another, and the slots 43 can extend as far as theleaf-spring joints 36 a and 36 b. This refinement once again results inhigh rotational mobility in the z-direction.

A further embodiment, which is illustrated in FIG. 8, also makes itpossible to provide for not only the center piece 36 c but also theleaf-spring joints 36 a and 36 b to be provided with slots 43. Thismeasure can be implemented in addition to or else independently of therefinement as shown in FIG. 7 with the slots 43. As can be seen, thisresults in a large number of small leaf springs or elastic intermediateparts which are arranged one behind the other in the y-direction.

As can be seen from FIG. 9, the first elastic intermediate parts 26 and31, which are like leaf springs, may each be replaced by a short tiltingjoint 26 a and 31 a, respectively. As can be seen, this is achieved byin each case one circular aperture 44 in the foot part 23, with theposition of the circular aperture 44 in each case being chosen such thatthis results in a constriction in the first intermediate part 26 or 31,respectively, and thus the tilting joint 26 a or 31 a, respectively.

As can also be seen from FIG. 9, the two second elastic intermediateparts 30 and 33, which are like leaf springs, can each be replaced bytwo short tilting joints, specifically in each case one lower tiltingjoint 30 a and 33 b and in each case one upper tilting joint 30 b and 33a, which are each separated by a connecting part 30 c, 33 c. In thiscase as well, the tilting joints are each formed by circular aperturesor incisions in the elastic intermediate parts, which in this way formdefined and short constrictions, and thus act as tilting joints.

As elastic intermediate parts, the leaf springs 26 and 30 need not beparallel to one another, as illustrated in FIGS. 3 and 4, but could alsobe at an angle to one another. This also applies to the leaf springs 31and 33 as elastic intermediate elements. A refinement such as this, ineach case with an angle γ which opens from the adjusting elements 27 and32 in the direction of the center part 24, can be seen in FIGS. 10 and11.

FIG. 12 shows a refinement of an adjustment device 21 which results in avery small physical height in the z-direction. As can be seen from theFigure, the two angles α in this case each correspond to an angle α ofthe leaf springs 26 and 31 as first elastic intermediate parts which isin each case greater than 90 degrees to the z-axis. In this case, theintersection of the planes of the leaf springs 30 and 33 as secondintermediate parts with the z-axis may be located outside the leafspring 36 as a third intermediate part, so that the local x and y-axesof the adjustment device 21 are also located outside the leaf spring 36.

However, for kinematics which are as advantageous as possible, theintersection of the planes of the leaf springs 30 and 33 as secondintermediate parts with the z-axis should as far as possible be locatedin the center of the leaf spring 36 which forms the third elasticintermediate part.

The adjustment device 21 illustrated in FIG. 12 may also be formed froma plurality of pieces. For this purpose, for example, the leaf spring 36is attached by the head part 25 as a separate part to the center part24.

The refinement with the angle α being greater than 90 degrees results inthe adjusting screws 28 and 29, as well as 34 and 35, not being arrangedon opposite sides of the adjusting elements 27 and 32, but in each casebeing located alongside one another, at a distance from one another, inwhich case they are in each case located on opposite sides of theleaf-spring plane 26 or 31, respectively, for operation of therespectively associated adjusting elements 27 and 32.

A further possible way to save physical height in the z-direction isillustrated in FIG. 13. For this purpose, the leaf spring 36 as thethird elastic intermediate part is arranged with the head part 25 offsetinwards in the x-direction with respect to the foot part 23 with theleaf springs 26, 30 and 31, 33 as the first and second intermediateparts and the adjusting levers 27 and 32. For this reason, the thirdelastic intermediate part 36 points downwards in a corresponding manner,and the head part 25 is located underneath (with respect to the footpart 23). This refinement allows the head part 25 to be arranged offsetin the x-direction at the same physical z-height alongside the foot part23.

In FIG. 13 as well, the adjustment device 21 is, for example, formedfrom a plurality of parts, with the location of the joint between theparts running in the center part 24.

As can be seen from FIGS. 14 and 15, the local z-axes of the threeadjustment devices 21 need not only be arranged parallel to the globalz₀-axis (optical axis), but can also be inclined with respect to it.

Other adjustment elements may, of course, also be provided foradjustment and fixing of the adjusting elements 27 and 32, instead ofadjusting screws 28, 29, 34 and 35, such as electromagnetic,piezo-actuator, pneumatic, magnetostrictive, hydraulic drives andsimilar mechanical motor drives.

FIG. 16 shows one exemplary embodiment of an operational situation whichis particularly advantageously of interest for rotationally symmetricaloptical elements when the optical element 8 need not be rotated foradjustment about the z₀-axis (optical axis), so that the angle of theoptical element 8 about the z₀-axis is always reset to zero if rotationabout the z₀-axis also occurs at the same time during linear movement bymeans of an adjustment device. Fundamentally, the illustrated exampleembodiment shown in FIG. 16 is designed in the same way as the exemplaryembodiments shown in FIGS. 6 to 9, so that the same reference symbolshave also been retained in this case. In the same way as in the case ofthe exemplary embodiments shown in FIGS. 6 to 9, the third intermediatepart 36 is also subdivided into two parts in this case, specificallyinto two leaf-spring joints 36 a and 36 b.

If the optical element 8 need be moved translationally only in the x₀,y₀ and z₀-directions, and need be tilted only about the x₀ and y₀-axes,while the rotation angle about the z₀-axis is always maintained at zero,the optical element 8 need be adjusted in only five degrees of freedom,rather than in six degrees of freedom.

If, in this case, the local z-axes of the adjustment devices 21 areparallel to the z₀-axis of the optical element 8, as is illustrated inFIGS. 2 and 3, and if the optical element 8 is not rotated about thez₀-axis, the rotational mobility of the head part 25 with respect to thefoot part 23 about the local z-axis can be restricted without any majoradverse effects on operation.

In the exemplary embodiments illustrated in FIGS. 2 to 13, the head part25 can be moved translationally in the x-direction with respect to thefoot part 23 by means of the adjustment devices 21, and can be tiltedabout the x, y and z-axes, with this mobility being made possible by themoving intermediate parts.

Subject to the conditions described above (no rotation about the z₀-axisof the optical element 8 and parallelity of the local z-axes withrespect to the z₀-axis), adjustment devices 21 can be used whose headpart 25 can be moved translationally in the x-direction and can betilted only about the x and y-axes, with respect to the foot part 23.The capability to rotate about the z-axis can be restricted in thiscase. This embodiment is illustrated in FIG. 16.

Since the mobility of the head part 25 with respect to the foot part 23is provided by the moving intermediate parts whose mobility is, however,not force-free but which is dependent on force, “parasitic” forcesduring adjustment of the adjustment devices 21 result in deformation ofthe inner ring 20, which can also be transferred to the optical element8, thus leading to undesirable imaging errors.

This disadvantageous deformation of the inner ring 20 and/or of theoptical element 8 may, however, be reduced by in each case making theelastic intermediate parts 26, 31, 30, 33 and 36 softer in thedirections in which they move.

In this sense, the exemplary embodiment shown in FIG. 16 is a furtherdevelopment of the embodiment illustrated in FIG. 9, in which betterx-translation mobility is achieved at the expense of z-rotation mobilityof the head part 25 with respect to the foot part 23.

In order to achieve this better x-translation mobility of the head part25 with respect to the foot part 23, the distance between theleaf-spring joints 36 a and 36 b of the third elastic intermediate part36 is increased in the z-direction.

As can be seen, of the two leaf-spring joints 36 a and 36 b, oneleaf-spring joint, as the upper leaf-spring joint 36 b, is arrangedbetween the center part 24 and the head part 25, and the otherleaf-spring joint, as the lower leaf-spring joint 36 a, is arrangedbetween the center part 24 and the foot part 23. Both leaf-spring joints36 a and 36 b can rotate and be tilted about the x-axis. This refinementin each case results in the lower leaf-spring joint 36 a being arrangedbetween the lower and upper tilting joints 30 a, 33 b and 30 b, 33 a.

The lack of the slots 43 in the center piece 36 c or the center, part 24increases the rotation resistance of the head part 25 with respect tothe foot part 23 about the z-axis. However, in the exemplary embodimentshown in FIG. 16, this is not associated with any adverse effects onoperation.

The movement of the leaf-spring joint 36 a to a position below the twoupper tilting joints 30 b and 33 a results in the connecting part 30 cin each case being split into two parts, that is to say the connectingparts 30 c and 30 d, and the connecting part 33 c being split into twoparts, that is to say the connecting parts 33 c and 33 d. In this case,the center part 24 then connects the leaf-spring joint 36 b to thetilting joint 30 b and to the tilting joint 33 a.

FIG. 17 shows the exemplary embodiment of an adjustment device asillustrated in FIG. 5, with additional statements having been made inorder to explain the subsequent figures, which relate to a positioningunit. The connection, which is in the form of a leaf spring andinteracts with the adjusting element in the form of an adjusting lever27, is illustrated in this figure as a coupler α with the rotationpoints A2 and B2, with the rotation point or rotating joint A2 producingthe connection to the adjusting lever 27, and the rotational point orthe rotating joint B2 producing the connection to the foot part 23. Acoupler b is located between the rotating joints A1 and the adjustinglever 27, and the rotating joint B1 and the center part 24. The sameapplies to the coupler c, which is located between the rotating joint C2and the adjusting element 32, and the rotating joint D2 to the foot part23 and the coupler D, which is located between the rotating joint C1 andthe adjusting lever 32, and between the rotating joint D1 and the centerpart 24.

FIG. 18 shows an embodiment in which the distances between A1 and B1, A2and B2, C1 and D1 as well C2 and D2 in each case shrink to zero and inwhich the couplers a, b, c and d now only form spring joint pairs.

Where the parts described in these figures and in the following figurescorrespond to the parts illustrated in FIGS. 2 to 16, the same referencesymbols have been adopted for them as well. Each positioning unit oradjustment device 21 once again has an x-axis, a y-axis and a z-axis ina local coordinate system, with the y-axis being oriented in thetangential direction, and the z-axis being oriented in the axialdirection.

The external holder 22 is firmly connected to adjacent holders or to anobjective structure, with the optical element 8 together with the threeadjustment devices 21 being positioned and adjusted with respect to theexternal holder 22, or the rest of the objective structure.

Each of the three adjustment devices 21 supports the inner ring 20together with the optical element 8 only in the tangential direction,that is to say in the y-direction, and in the axial direction, that isto say in the z-direction, so that the three adjustment devices 21together result in a statically defined mounting for the inner ring 20and thus also for the optical element 8, because the six degrees offreedom of the inner ring 20 are supported by in each case two forcesper adjustment device 21.

Each adjustment device 21 is subdivided into the foot part 23, one ormore center parts 24 a, 24 b, 24 c, the head part 25 and the twoadjusting levers 27 and 32, which are connected to one another viatilting-spring joints 45 a, 46 a, 45 b, 46 b.

In order that only one force is transmitted in the y-direction and inthe z-direction per adjustment device 21, the head part 25 must betranslationally flexible with respect to the foot part 23 in thex-direction, and must be capable of tilting about the x, y and z-axes.

The adjusting lever 32 is in this case mounted by means of atilting-spring joint 45 a, whose tilting axis is oriented parallel tothe x-axis, such that it can rotate in the foot part 23, in which casethe angle of the adjusting lever 32 with respect to the foot part 23 canbe set and fixed by means of the adjusting screws 34 and 35. Atilting-spring joint 46 a which is offset with respect to thetilting-spring joint 45 a in the y-direction and is arranged parallel toit connects the adjusting lever 32 to the center part 24 a. The twotilting axes of tilting-spring joints 47 and 48 which are oriented inthe y-direction and are offset in the z-direction allow the center part24 c to be moved translationally in the x-direction and to be tiltedabout the y-axis with respect to the center part 24 a, thus alsoallowing the head part 25 to be moved translationally in thex-direction, and to be tilted by a y-axis, with respect to the foot part23. A tilting-spring joint 49, whose tilting axis is oriented parallelto the x-axis, connects the center part 24 c to the head part 25, sothat the head part 25 can be tilted about the x-axis with respect to thecenter parts 24 and thus also with respect to the foot part 23.

A (slight) rotational flexibility of the head part 25 with respect tothe foot part 23 can be achieved by torsion of the tilting-spring joints47, 48 and 49. The head part 25 of each adjustment device 21 can thus bemoved translationally in the x-direction, and can be tilted about the x,y and z-axes, with respect to the foot part 25.

In order to allow the optical element 8 to be moved in all six degreesof freedom with respect to the external holder 22, it must be possibleto move the head part 25 on the yz-plane with respect to the foot part23 for each of the three adjustment devices 21, in the same way, forexample, as in the case of a hexapod principle, or a Stuart platform.

FIG. 19 illustrates the adjustment options (which will be explained inmore detail in the following text) in an outline illustration with thetwo adjusting levers 27 and 32 as levers, and the tilting-spring joints45 a, 46 a and 45 b, 46 b. The two adjusting levers 27 and 32 each havea respective force arm 27 a and 32 a, on which the respective adjustingscrews 28 and 29 as well as 34 and 35 act as adjusting elements oractuators. The tilting-spring joints 45 a and 45 b represent the leverbearings for the adjusting levers 27 and 32. The tilting-spring joints46 a and 46 b form the coupling points to the centre point 24. A firstconnecting area A (head part 25) for connection to the optical element,and a second connecting area B (foot part 23) for connection to anobject in the vicinity of the optical element, in this case to theholder 22, and the intermediate element C (center part 24) which acts onthe two tilting-spring joints 46 a and 46 b form a framework.

On deflection of one or else both force arms 27 a and 32 a with in eachcase one rotational point about the respectively associated leverbearing 45 a and 45 b, the framework is deflected in a correspondingmanner via the two load arms 27 b and 32 b of the two adjusting levers27 and 32. If operated on one side, as illustrated by the actuator 29,this results in the connecting area A (end part 25) being tilted on acircular arc. If the two adjusting levers 27 and 32 are operated at thesame time, this results in a lifting or lowering movement of theconnecting area A along the z-axis. The hinged joints which areassociated with the two adjusting levers 27 and 32 have approximatelyparallel rotation axes which, in a first position, lie approximately ona plane. In the position illustrated in FIG. 19, this is the basicposition, while the dashed illustration represents a deflected, secondposition.

As can be seen, in the basic position, the approximately parallelrotation axes lie at least approximately on a plane, with the centerpart 24 a, on which the two tilting-spring joints 46 a and 46 b act,being located in between. The distance between the rotation axes of thetwo adjusting levers, in each case between the rotation axes and,respectively, tilting-spring joints 45 b and 46 b as well as 45 a and 46a, respectively, is less than 0.1 times, and preferably less than 0.01times, the lever distance of the force arm (distance between theactuators 28/29 and the tilting-spring joint 45 b as the lever bearing,or the two actuators 34/35 and the tilting-spring joint 45 a as thelever bearing). Alternatively or additionally, the maximum distancebetween the plane which is covered by the rotation axes of the twoadjusting levers 45 a and 45 b and a plane which is covered between thetilting-spring joints 46 b and 46 a is less than 0.1 times, andpreferably less than 0.01 times, the distance between the rotation axes45 a, 45 b of the two adjusting levers 27 and 32.

If, according to the embodiment shown in FIG. 20, the adjusting lever 32is moved by means of the adjusting screws 34 and 35 with respect to thefoot part 23, then the adjusting lever 32 is tilted about thetilting-spring joint 45 a, with the tilting-spring joint 46 a beingraised or lowered owing to the y-offset with respect to thetilting-spring joint 45 a in the z-direction—depending on the directionin which the adjusting lever 32 is tilted.

Since the z-movement of the tilting-spring joint 46 a is transmitted tothe center part 24 a, while on the other hand the center part 24 a isheld fixed on the tilting-spring joint 46 b by means of the adjustinglever 27, the center part 24 a has to rotate about the tilting-springjoint 46 b. This rotation results in the head part 25 carrying out apivoting movement on the yz-plane, to be precise likewise about thetilting-spring joint 46 b.

When the adjusting lever 27 is tilted as shown in FIG. 21, this resultsin a pivoting movement, reflected with respect to the z-axis, of thehead part 25, as is caused by tilting of the adjusting lever 32 as shownin FIG. 5.

A y-movement or a z-movement of the head part 25 with respect to thefoot part 23 may be composed of a linear combination of the two pivotingmovements shown in FIGS. 5 and 6.

The structures according to the invention result in a solid-jointmeasurement which is highly resistant to shock and is at the same timehighly stiff, so that the optical element 8 cannot as easily be excitedto carry out undesirable oscillations. Stiffer actuators andmanipulators can be provided in particular in the y and z directions,with greater flexibility in the other directions. This is important, forexample, in order to allow compliance with the dynamic requirements forlarge, heavy optical elements, such as mirrors.

It is not absolutely essential for the head part 25 to be able to rotatewith respect to the foot part 23 about the z-axis if the optical element8 need not be rotated about the z-axis.

Instead of a connection of the head part 25 to an internal holder 20, itis, of course, also possible for the head part 25 to be attacheddirectly to the optical element 8.

FIG. 22 shows an embodiment in which the center part 24 b is subdividedby means of separating cuts in the z-direction between thetilting-spring joints 47 and 48, whose tilting axis is oriented parallelto the y-axis, in order to achieve greater rotation flexibility aboutthe z-axis.

For clarity reasons and for simplification, only the reference symbolsfor the most important parts and for the new features are indicated inFIG. 22 and in FIGS. 23 to 29, which will be described in the followingtext.

FIG. 23 illustrates an embodiment in which the tilting-spring joints 47and 48 and the center part 24 b are replaced by a leaf spring 50, whoseplane lies on the yz-plane.

Various combinations and arrangements are possible for the spring jointsbetween the center part 24 a and the head part 25, provided that theseallow the head part 25 to be moved translationally in the x-directionand to be tilted about the y-axis and z-axis with respect to the centerpart 24 a. For example, as shown in FIG. 24, the positions of thetilting-spring joints 48 and can thus be interchanged in comparison withthe embodiment shown in FIG. 18.

In the same way, as shown in the embodiment in FIG. 25, the positions ofthe tilting-spring joints 47 and those of the tilting-spring joint 48can likewise be interchanged.

As can be seen from FIG. 26, the tilting-spring joint 49 can bestiffened in the y-direction by additionally connecting the head part 25to the center part 24 c via a hinged-joint coupler, comprising thehinged joints 491 a, 491 b and a center piece 491 c, with thehinged-joint planes of the hinged joints 491 a and 491 b intersectingthe hinged-joint plane of the tilting-spring joint 49 on the tiltingaxis of the head part 25 with respect to the center part 24 c.

The head part 25 can be connected to the center part 24 c via a furtherhinged-joint coupler, comprising the hinged joints 492 a, 492 b and acenter piece 492 c, with the hinged-joint planes of the hinged joints492 a and 492 b intersecting the hinged-joint plane of thetilting-spring joint 49 on the tilting axis of the head part 25 withrespect to the center part 24 c.

The hinged-joint couplers comprising the hinged joints 491 a, 491 b andthe center piece 491 c can also be replaced by a leaf spring (notillustrated), with the plane of the leaf spring intersecting thehinged-joint plane of the tilting-spring joint 49 on the tilting axis ofthe head part 25 with respect to the center part 24 c.

The hinged-joint coupler, comprising the hinged joints 492 a, 492 b andthe center piece 492 c, can likewise be replaced by a leaf spring (notillustrated), with the plane of the leaf spring intersecting thehinged-joint plane of the tilting-spring joint 49 on the tilting axis ofthe head part 25 with respect to the center part 24 c.

As can be seen from FIG. 27, the tilting-spring joint 45 a can bereinforced by a hinged joint 451 while retaining the original tiltingaxis of the tilting-spring joint 45 a, by the planes of thetiling-spring joints 45 a and 451 intersecting on the tilting axis ofthe tilting-spring joint 45 a.

The tilting-spring joint 45 b can be reinforced by means of a hingedjoint 452 while retaining the original tilting axis of thetilting-spring joint 45 b, by the planes of the hinged joints 45 b and452 intersecting on the tilting axis of the tilting-spring joint 45 b.

FIG. 28 shows how the tilting-spring joint 46 a can be reinforced by ahinged joint 461 while retaining the original tilting axis of thetilting-spring joint 46 a, by the planes of the hinged joints 46 a and461 intersecting on the tilting axis of the tilting-spring joint 46 a.

The tilting-spring joint 45 b can be reinforced in the same way by ahinged joint 462 while retaining the original tilting axis of thetilting-spring joint 46 b, by the planes of the hinged joints 46 b and462 intersecting on the tilting axis of the tilting-spring joint 46 b.

According to the exemplary embodiment shown in FIG. 29, the adjustmentdevice 21 can be stiffened by connecting the center part 24 a to thefoot part 23 in the y-direction by means of a hinged-joint coupler,comprising the hinged joints 241 a, 241 b and the center piece 241 c, inwhich case the plane of the hinged joints 241 a and 241 b should lieapproximately on a straight line which is formed by the tilting-springjoints 45 a, 45 b, 46 a and 46 b.

The center part 24 a can also be connected to the foot part 23 via afurther hinged-joint coupler, comprising the hinged joints 242 a, 242 band the center piece 242 c, in which case the plane of the hinged joints242 a and 242 b should lie approximately on a straight line which isformed by the tilting-spring joints 45 a, 45 b, 46 a and 46 b.

The hinged-joint coupler comprising the hinged joints 241 a, 241 b andthe center piece 241 c can also be replaced by a leaf spring (notillustrated), in which case the plane of the leaf spring should lieapproximately on a straight line which is likewise formed by thetilting-spring joints 45 a, 46 a, 45 b, 46 b.

In the same way, the hinged-joint coupler comprising the hinged joints242 a, 242 b and the center piece 242 c can be replaced by a leaf spring(likewise not illustrated), in which case the plane on this leaf springshould likewise lie approximately on a straight line which is likewiseformed by the tilting-spring joints 45 a, 46 a, 45 b, 46 b.

FIG. 30 shows an enlargement of a detail of the lever 26 which is like aleaf spring and is connected to the foot part 23, and of the lever 30which is like a leaf spring and is connected to the center part 24. Ascan be seen, a stiffening element 52 for adjustment of the stiffness ofthe hinged-joint connection is located in the gap 51 between the twolevers 26 and 30, which are like leaf springs. The stiffening element 52may, for example, be a piezo-element which can be activated electricallyand is arranged with play in the gap 51 when not activated. When thepiezo-elements are activated, the stiffening element 52 is “thickened”,so that the gap 51 is bridged, so that the play is changed by higherstiffness, until the play is completely changed by closure of the gap.

At least one of the lever bearings 45 a/45 b and/or one tilting-springjoint 46 a/46 b of the two load arms 32 b or 27 b, respectively, of thetwo adjusting levers 32 and 27 may be designed such that, when thelevers are deflected, the lever bearings carry out a rolling movementalong a curved path, which is designed to be relatively stiff incomparison to at least one connecting area A, B or the intermediateelement C, on a respective contact bearing 53, as is indicated in FIG.31 (see also the arrow 54).

A similar refinement results from the lever bearing 45 b which isillustrated in FIG. 32. As can be seen, the lever bearing 45 b ismounted on an elastically flexible cap 55, thus likewise resulting in amovement on a curved path corresponding to the arrow 54 when theassociated adjusting lever 27 is deflected.

In the embodiments illustrated in FIGS. 18 and 20 to 32, elasticdeformation at the tilting-spring joints of the two adjusting levers 27and 32 may also be sufficient on the basis of the natural elasticity forthe minor adjusting and adjustment movements which occur inmicrolithography.

By way of example, each of the two load arms 27 b and 32 b of the twoadjusting levers 27 and 32, respectively, or else the center part 24 a,may likewise be in the form of a deformable compensating element. Thisalso applies to the two force arms 27 a and 32 a.

1. A positioning unit for an optical element in a microlithographicprojection exposure installation having a first connecting area A forconnection to the optical element (8), and a second connecting area Bfor connection to an object in the vicinity of the optical element, atleast two levers (27, 32), which are connected via their respectivelever bearings (45 a, 45 b) to the second connecting area B, and whoserespective load arm (27 b, 32 b) is connected by means of a hinged joint(46 a, 46 b) and via an intermediate element C, which acts on thishinged joint, to the first connecting area A, having adjustment devicesor actuators (28, 29, 34, 35) arranged on the respective force arms (27a, 32 a) of the levers (27, 32) in which, in a first position, the firstconnecting area A and the second connecting area B are arranged relativeto one another such that the lever. bearings (45 a, 45 b) of the atleast two levers (27, 32) and the hinged joints (46 a, 46 b) which areassociated with these levers have approximately parallel rotation axes,which lie approximately on one plane in the first position.